1. Field of the Invention
This invention relates generally to a miniature electric rotating machine, and more particularly to a permanent magnet field system to be adopted to a rotating machine of a permanent magnet field system, or to an electric rotating machine of a permanent magnet field system equipped with auxiliary poles of the type in which a field pole is constituted by a permanent magnet and auxiliary poles of a magnetic material.
2. Description of the Prior Art
Permanent magnet field system DC machines using a permanent magnet for poles are known in the art. The permanent magnet used for DC machines of this type has generally an arc shape and the magnet is an anisotropic magnet. The permanent magnet is magnetized by a magnetizer such as that disclosed in Japanese Patent Laid-Open No. 43167/1983 entitled "Magnetizer of Field System Aggregate" which was laid open on Mar. 12, 1983. The magnet is magnetized in anisotropic directions substantially towards the center in a radial direction. Therefore, a problem occurs that when the magnetic flux of armature reaction due to an armature current acts, the permanent magnet disposed on a demagnetizing side is demagnetized. This means that the thickness of the permanent magnet must be increased.